Generally, the development relates to systems and processes involving the utilization of repeatable magnetic stripe characteristics to verify magnetic stripe-bearing documents.
Various forms of cards bearing a magnetic stripe (magstripe cards) have long been used for a variety of different purposes. Such cards are currently used in large numbers, for example in the forms of credit cards, debit cards, tickets, passes, I. D. cards and so on. Typically the magnetic stripes of such cards carry recorded data relating to the use of the card, and in some instances relating to the assigned user or owner of the card.
Although magnetic stripe cards are widely and successfully used in commerce and industry, counterfeiting and modification of cards (along with other forms of documents) are common occurrences. The resulting losses are great. Consequently, a continuing need exists for a practical system and method to reliably verify the authenticity of documents generally, and specifically of magnetic stripe cards. That is, a substantial need exists for techniques and apparatus to reliably determine whether a presented magstripe card is authentic.
Over the years, there have been numerous proposals for verifying documents, including the authenticity of magnetic stripe cards. A substantial number of prior proposals have been based on a concept of using certain magnetic characteristics of the magnetic stripe to identify cards. In that regard, it has been determined that generally, the magnetic stripes of individual cards possess inherent, substantially unique, magnetic characteristics that can be repeatedly sensed. Over the years, these characteristics sometimes have been recognized as contributing a noise component to sensed signals. Thus, along with the signal component representing recorded data, a repeatable noise signal component also appears. Just as the magnetic characteristics of individual stripes are distinct, noise signals are somewhat unique among cards. Accordingly, it has been proposed to employ such magnetic characteristics and the resulting signals as a basis for identifying individual magnetic stripe cards. Generally, note that in sensing magnetic stripes, the length of a magstripe translates into a time scale for the sensed signal. Thus, specific portions of the sensed signal represent specific areas of the magstripe.
In general, a variety of verification techniques and structures, based on the noise or characteristic component of a sensed magstripe signal have been proposed. In some instances, the general technique has been compared to the science of human fingerprinting, that is, involving the use of representations of a somewhat unique physical characteristic for purposes of identification.
One prior magstripe identification proposal involved using a separate non-data magnetic stripe placed on a document specifically for purposes of identifying the document. Other proposals have involved various treatments involving the signals that are variously recorded conditioned and sensed from magnetic stripes.
Typically, the magstripes on conventional magstripe cards are divided into parallel tracks that are separately recorded. Many of the prior proposals for document authentication have involved the techniques for recording a track of the magnetic stripe with digital data to provide representative magnetic transitions along the length of the magnetic stripe. Signals sensed from the magnetic transitions, or other portions of the signal were then proposed for characterizing a card or other document. For example, the characteristics of peaks in the sensed magnetic signal (representing magnetic transitions) have been proposed to be used for identifying documents bearing a magnetic stripe.
Other proposals have suggested using other portions of the sensed magstripe signal from one of the tracks. For example, the relatively flat signal portions representative of magnetized regions of the stripe that are located between magnetic transitions have been proposed for use.
Various techniques also have been proposed for attaining more consistent results in sensing characteristic signals, for example: averaging the results of multiple sensings, oversampling (increased sampling as by a factor of one hundred), and using a phase locked loop to control sampling. It also has been opined that for identification purposes, sizable variations are acceptable between individual sensings of magstripe characteristics.
In spite of the various structures and techniques proposed for magstripe fingerprinting, the concept has not gained widespread acceptance. That is, using the remanent noise in the signal sensed from magstripes to verify individual documents has not come into widespread use. Rather, although numerous proposals have been suggested for using the magnetic noise to characterize documents, the technique simply has not gained significant commercial or industrial acceptance.
In general, the system of the present invention is based on recognizing the various problems of using the repeatable characteristics of a magstripe for purposes of document identification, for example in broad commercial and industrial applications. In that regard, many problems arise in the industrial and commercial arenas which are not apparent in the laboratory. Several of those problems are distinctly associated with the plastic magstripe cards typically used as bank transaction cards.
One major consideration relating to the extensive use of magnetic characteristics for card recognition involves the number of cards in a system. For example, a typical commercial system must readily accommodate many thousands of individual cards operating randomly in combination with hundreds, if not thousands, of individual processing units.
Furthermore, in extensive systems, reliability becomes exceedingly important, particularly in the realms of financial and security transactions, as are involved with bank cards.
In general, the system of the present invention involves improvements that enable magnetic characteristic verification techniques to operate successfully in the realms of widespread commercial and industrial applications. Specifically, the processes and systems of the present invention are directed to improved sensing structures for magnetic stripe cards and to improved processes for consistently locating and processing specific magnetic stripe characteristic features as well as developing a magnetic stripe identification characteristic from such features.
In accordance with the present system implementing processes hereof, repeatable magnetic characteristic signals (resulting from specific characteristic features of the magstripe) are selected from defined areas of a digitally-recorded magnetic stripe. The defined areas are located between magnetic data transitions. Such defined areas of the stripe may be magnetized to a level of saturation and accordingly produce relatively flat (stable) sections of the sensed magnetic analog signal. Although these signal sections are relatively flat, they still manifest a low level signal (noise) representative of the repeatable magnetic characteristics or features of the stripe. Thus, these signal sections can be used to truly identify each magnetic stripe in a manner somewhat analogous to a fingerprint.
In accordance herewith, after sensing a magstripe to produce a magnetic analog signal, a target number of samples are taken from several relatively flat sections of the analog signal using a frequency lock loop. The set or group of individual samples for each section are converted to a digital form, then selectively processed to obtain a predetermined subset of samples. The predetermined subset of digitized samples is then further processed by offset selection to accomplish a sub-subset of digitized samples that become a component of a magnetic characteristic designation. That is, several sub-subsets of digitized samples are combined to form a magnetic designation or identifier for the magstripe-bearing card. With the characteristic identifier for a card available as a reference, a freshly generated identifier can be tested by correlation to indicate the authenticity of the card.
In view of the relatively small amplitude of the magnetic characteristic signal component, spuriously generated signals can present a significant problem. In that regard, a source of spurious signals has been identified that results from the typical form of contemporary magnetic transducer heads. Consequently, an improved head is disclosed in accordance herewith to reduce certain troublesome spurious signal components in the magstripe analog signal.